Tropospheric ozone events observed at the summit of Mount Fuji (3776 m
above sea level) were analyzed as case studies. The ozone, intruding
from the lower stratosphere by the cutoff low or the tropopause fold o
ver the Asian continent, is transported to the middle troposphere over
Japan even in summer. The subtropical jet, which is intensified over
Japan, also contributes to the summer intrusion from the stratosphere.
A long stratospheric streamer, as described previously by Appenzeller
et al. , brings about a persistent ozone enhancement at the sum
mit of Mount Fuji. The large variation of summer ozone over Japan is a
ttributable to the alternate overspreading of these ozone-rich stratos
pheic air masses and the ozone-depleted subtropical maritime air mass.
In contrast, winter ozone variation is relatively small at the summit
of Mount Fuji. The steep potential temperature gradient between 500 h
Pa and 300 hPa in the winter cutoff low, which restrains vertical mixi
ng in the upper troposphere, possibly causes less influence of the str
atospheric air mass on the middle troposphere in winter, since mixing
processes around a cutoff low play an important role in air mass excha
nge between the stratosphere and the troposphere.